Rigid polyurethane foams are good insulating materials and are excellent in moldability and processability. Therefore, they are widely used in various; fields, for example as insulating materials for refrigerators, buildings, low-temperature warehouses, storage tanks, refrigerator ships, pipes and so forth. They have been improved in thermal conductivity year by year. At present, they can have a thermal conductivity as low as about 0.015 W/mK on the commercial product level and thus show the best insulator performance among heat insulating materials used at around normal temperature. However, the requirement that the insulating materials should have a still lower thermal conductivity is increasing with the recent request for much more energy saving.
In producing rigid polyurethane foams, the so-called one-shot process is generally used which comprises mixing a composition (A) comprising, as main components thereof, a polyol, a catalyst, a foam controlling agent (cell stabilizer) and a blowing agent with a composition (B) comprising, as a main component thereof, an organic polyisocyanate and thus causing the foaming process and curing process to proceed in parallel for foam formation.
A typical example of the blowing agent used in such rigid polyurethane foam production is trichlorofluoromethane (R-11). R-11 is often used in combination with water, which is a chemical blowing agent capable of reacting with isocyanates to generate carbon dioxide. However, the conventional chlorofluorocarbon (CFC) blowing agents, typically R-11, are chemically stable and therefore, as heretofore pointed out, can diffuse far into the stratosphere and destroy the ozone layer. The result would be that ultraviolet radiation from the sun be not absorbed in the ozone layer but reach the surface of the earth, causing skin ,cancer and so on. Such is now a serious global-scale environmental problem. Therefore, the use of CFCs has been restricted since 1989. Of course, the use of R-11 in urethane foam production is now under control.
Accordingly, various investigations have been made in search of blowing agents capable of serving as alternatives for CFC gases. Thus, HCFC-141b, for instance, has been nominated as a candidate alternative for CFCs.
However, it is already known that when HCFC-141b is used, for instance, as a blowing agent in producing rigid polyurethane foams by the conventional method, 1-chloro-1-fluoroethane (hereinafter referred to as HCFC-151a) is formed as a result of reduction and/or 1-chloro-1-fluoroethene (hereinafter referred to as HCFC-1131a) as a result of dehydrochlorination. The physical properties and toxicities of these decomposition products are still unknown in many aspects, hence might be hazardous to the environment.